Method and apparatus to control temperature of an exhaust aftertreatment system for a hybrid powertrain

ABSTRACT

An internal combustion engine is fluidly connected to an exhaust aftertreatment system and operatively connected to an electro-mechanical transmission to transmit tractive power to a driveline. The engine is controlled during an engine operating cycle by determining a temperature of the exhaust aftertreatment system and adjusting power output of the engine based upon the temperature of the exhaust aftertreatment system and a preferred temperature range of the exhaust aftertreatment system. The electro-mechanical transmission is controlled to transmit tractive power to the driveline to meet an operator torque request based upon the adjusted power output of the engine.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/985,981 filed on Nov. 7, 2007 which is hereby incorporated herein byreference.

TECHNICAL FIELD

This disclosure pertains generally to control systems for hybridpowertrain systems.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Powertrain control systems, including hybrid powertrain architectures,operate to meet operator demands for performance, e.g., torque andacceleration. The operator demands for performance are balanced againstother operator requirements and regulations, e.g., fuel economy andemissions. The balance of operator demands for performance against otheroperator requirements and regulations can be accomplished by quantifyingengine power losses associated with specific operating conditions duringongoing operation.

Known systems to determine instantaneous engine power losses utilizepre-calibrated tables stored in on-board computers to determine lossesbased upon measured operating conditions during operation. Such systemsconsume substantial amounts of computer memory. The memory space isfurther compounded by engine operating modes, e.g., cylinderdeactivation. Such systems are not able to accommodate variations inoperating conditions, including engine warm-up and warm-up of exhaustaftertreatment systems.

SUMMARY

An internal combustion engine is fluidly connected to an exhaustaftertreatment system and operatively connected to an electro-mechanicaltransmission to transmit tractive power to a driveline. The engine iscontrolled during an engine operating cycle by determining a temperatureof the exhaust aftertreatment system and adjusting power output of theengine based upon the temperature of the exhaust aftertreatment systemand a preferred temperature range of the exhaust aftertreatment system.The electro-mechanical transmission is controlled to transmit tractivepower to the driveline to meet an operator torque request based upon theadjusted power output of the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an exemplary architecture for apowertrain and a control system, in accordance with the presentdisclosure;

FIG. 2 is a schematic depiction, in accordance with the presentdisclosure; and

FIGS. 3A and 3B are graphical data, in accordance with the presentdisclosure.

DETAILED DESCRIPTION

Referring now to the drawings, wherein the showings are for the purposeof illustrating certain exemplary embodiments only and not for thepurpose of limiting the same, FIG. 1 depicts a schematic diagram of anexemplary powertrain and control system operative to execute controlroutines. The powertrain comprises an internal combustion engine 14 andfirst and second electric machines (‘MG-A’) 56 and (‘MG-B’) 72. Theinternal combustion engine 14 and the first and second electric machines56 and 72 each generate power transmitted via the transmission 10 to anoutput member 64, e.g., a driveline for a vehicle (not shown). The powergenerated by the engine 14 and the first and second electric machines 56and 72 and transmitted to the transmission 10 is characterized anddescribed in terms of input torques, referred to herein as Ti, T_(A),and T_(B), respectively, and speeds, referred to herein as Ni, N_(A),and N_(B), respectively.

The engine 14 comprises a multi-cylinder internal combustion engineselectively operative in several states to transmit power to thetransmission 10 via an input member 12, e.g., a rotating shaft. Theengine 14 can be a spark-ignition engine, a compression-ignition engine,a spark-ignition engine selectively operative in a controlledauto-ignition mode, and other engine configurations. The engine 14includes a crankshaft operatively coupled to the input member 12 of thetransmission 10. A rotational speed sensor monitors rotational speed ofthe input member 12. The engine 14 is monitored and controlled by anengine control module (hereafter ‘ECM’) 23. An engine operating point,comprising an engine rotational speed N_(E) and an output torque T_(E)is indicative of power output of the engine 14. The engine operatingpoint can differ from the input speed Ni and the input torque Ti to thetransmission 10 due to placement of torque-consuming components on theinput member 12 between the engine 14 and the transmission 10, e.g., ahydraulic pump and/or a torque management device.

The engine 14 is fluidly connected to an exhaust aftertreatment system16 comprising one or more devices adapted to oxidize and/or reduce (i.e.convert) engine exhaust gas feedstream constituents to inert gasesand/or trap particulate matter. Exemplary exhaust gas feedstreamconstituents of interest can include hydrocarbons (hereafter ‘HC’),carbon monoxide (hereafter ‘CO’), nitrides of oxygen (hereafter ‘NOx’),and particulate matter (hereafter ‘PM’). The device(s) of the exhaustaftertreatment system 16 are configured to operate within conditionscharacterized by a preferred temperature range and a preferred flow rateover which conversion efficiency of one or more of HC, CO, NOx, and PMcan be optimized. When the exhaust aftertreatment system 16 is exposedto and operates at temperatures that are below the preferred temperaturerange, one result can include reduced conversion efficiency for theexhaust gas constituents, including oxidation of HC and CO, reduction ofNOx, and combustion of PM. When the exhaust aftertreatment system 16 isexposed to and achieves temperatures that are greater than the preferredtemperature range, one result can include thermal damage. When theengine 14 is a spark-ignition engine operating primarily at astoichiometric air/fuel ratio, the exhaust aftertreatment system 16 caninclude elements comprising a three-way catalytic converter, having alight-off temperature of about 300° C. and a preferred temperature rangethat is between about 300° C. and about 600° C. When the engine 14 is aspark-ignition engine selectively operating at a stoichiometric air/fuelratio and at a lean air/fuel ratio, the exhaust aftertreatment system 16can include elements comprising a three-way catalytic converter and alean-NOx adsorber device which can have a preferred temperature rangebetween about 250° C. and about 500° C. and a preferred short-termoperating temperature of above about 600° C. for regeneration. When theengine 14 is a compression-ignition engine, the exhaust aftertreatmentsystem 16 can include elements comprising a lean-NOx adsorber device, anoxidation catalytic converter having a light-off temperature of about300° C. and a preferred temperature range that is between about 300° C.and about 600° C., and a particulate trap which can have a preferredoperating temperature range that is between about 250° C. and about 500°C. and a preferred short-term operating temperature above about 600° C.for regeneration. When the engine 14 is a spark-ignition engineselectively operative at a lean air/fuel ratio and in a controlledauto-ignition combustion mode, the exhaust aftertreatment system 16 caninclude a three-way catalytic converter, a lean-NOx adsorber device, anda particulate trap. The forgoing descriptions are intended to beillustrative of elements and configurations of the elements for theexhaust aftertreatment system 16, and not an exhaustive description ofavailable configurations.

Engine operation is described in terms of the engine operating point,engine operating modes, and engine states in which the engine 14 can beselectively operated. The engine operating modes include air/fuel ratiooperation at one of a stoichiometric operating mode and a rich operatingmode. The air/fuel ratio operation may additionally include a leanoperating mode when the engine 14 is operating as a compression-ignitionengine or the engine 14 is a spark-ignition engine operating in acontrolled auto-ignition combustion mode. The engine operating modesalso include engine temperature management comprising a catalyst warm-upmode and a warmed-up catalyst mode, which can be based upon temperatureof the exhaust aftertreatment system 16 as discussed in further detailwith reference to FIGS. 3A and 3B.

The engine warm-up mode includes engine operating control routinescomprising retarding spark ignition timing when the engine 14 comprisesa spark-ignition engine, and retarding fuel injection timing when theengine 14 comprises a compression-ignition engine, during engineoperation after starting to increase combustion heat generated by theengine 14. The increased heat generated during combustion can betransferred to the aftertreatment system 16. The engine states comprisea normal engine state and a cylinder deactivation state. In the normalengine state, all the engine cylinders are fueled and fired. In thecylinder deactivation state, typically half of the cylinders, e.g., onebank of a V-configured engine, are deactivated. A bank of cylinders canbe deactivated by discontinuing fuel injection thereto and deactivatingvalves.

The first and second electric machines 56 and 72 each comprise athree-phase AC electric machine having a rotor rotatable within astator. An electrical energy storage device (hereafter ‘ESD’) 74 is highvoltage DC-coupled to a transmission power inverter module (hereafter‘TPIM’) 19 via DC transfer conductors 27. The TPIM 19 is an element ofthe control system.

The transmission 10 preferably comprises a device including the inputmember 12 operatively coupled to the crankshaft of the engine 14, one ormore planetary gear sets, one or more torque-transmitting devices (e.g.clutches, brakes), and the output member 64. The stators of each of thefirst and second electric machines 56 and 72 are grounded to a case ofthe transmission 10, and the rotors are operatively coupled to rotatingelements of the planetary gear sets to transmit torque thereto. Anelement of one of the planetary gear sets is operatively coupled to theinput member 12, and an element of one of the planetary gear sets isoperatively coupled to the output member 64. The transmission 10receives input power from the torque-generative devices, including theengine 14 and the first and second electric machines 56 and 72 as aresult of, respectively, energy conversion from fuel or electricalpotential stored in the ESD 74. Tractive power transmitted through thetransmission 10 is output to the driveline through the output member 64.

The control system described herein comprises a subset of an overallvehicle control architecture, and provides coordinated system control ofthe powertrain. The control system synthesizes pertinent information andinputs, and executes algorithms to control various actuators to achievecontrol targets of fuel economy, emissions, performance, driveability,and protection of hardware, including batteries of ESD 74 and the firstand second electric machines 56 and 72. The distributed control modulesystem includes the ECM 23, a transmission control module (hereafter‘TCM’) 17, a battery pack control module (hereafter ‘BPCM’) 21, and theTPIM 19. A hybrid control module (hereafter ‘HCP’) 5 providessupervisory control and coordination of the ECM 23, the TCM 17, the BPCM21, and the TPIM 19. A user interface (‘UI’) 13 is operatively connectedto a plurality of devices through which a vehicle operator controls ordirects operation of the powertrain. The devices include an acceleratorpedal 113 (‘AP’) from which an operator torque request is determined, anoperator brake pedal 112 (‘BP’), a transmission gear selector 114(‘PRNDL’), and, a vehicle speed cruise control (not shown). Thetransmission gear selector 114 may have a discrete number ofoperator-selectable positions to enable one of a forward and a reversedirection of the output member 64.

The ECM 23 is operably connected to the engine 14, and functions toacquire data from a variety of sensors and control a variety ofactuators, respectively, of the engine 14 over a plurality of discretelines collectively shown as aggregate line 35. The ECM 23 monitorsengine operating conditions, comprising monitoring inputs from variousengine sensing devices and engine operation to determine engine speed(RPM), engine load (Brake Torque, N-m), barometric pressure, and enginecoolant temperature. Engine sensing devices operative to monitor engineoperating conditions comprise a crankshaft sensor from which the ECM 23determines the engine speed, N_(E) (RPM), and a mass air flow sensorwhich the ECM 23 utilizes in determining the engine torque T_(E) or load(e.g., NMEP in N-m). Engine load is also determinable from monitoringoperator input to the accelerator pedal 113. Engine sensing devicesfurther include a coolant temperature sensor from which the ECM 23monitors engine temperature, and an exhaust gas sensor from which theECM 23 monitors the exhaust gas feedstream, e.g., air/fuel ratio,temperature, or exhaust constituents. The ECM 23 monitors engineoperating conditions, including the engine speed (RPM), the load (braketorque or NMEP in N-m), barometric pressure, coolant temperature, andthe exhaust gas, e.g., air/fuel ratio. The engine air/fuel ratio can bemeasured directly with a sensor or estimated based upon engine operatingconditions. The ECM 23 can execute algorithmic code to estimate atemperature of the elements of the exhaust aftertreatment system 16based upon the engine operating conditions. Alternatively, one or moretemperature sensing devices can be adapted to monitor temperature of oneof the elements of the exhaust aftertreatment system 16. The ECM 23generates and communicates command signals to control engine actuators,including, e.g., fuel injectors, ignition modules, and throttle controlmodules.

The TCM 17 is operably connected to the transmission 10 and functions toacquire data from a variety of sensors and provide command signals tothe transmission 10, including monitoring inputs from pressure switchesand selectively actuating pressure control solenoids and shift solenoidsto actuate clutches to achieve various transmission operating modes. TheBPCM 21 is signally connected to one or more sensors operative tomonitor electrical current or voltage parameters of the ESD 74 toprovide information about the state of the batteries to the HCP 5. Suchinformation includes battery state-of-charge (‘SOC’), battery voltage,amp-hour throughput, and available battery power.

The TPIM 19 transmits electrical power to and from the first electricmachine 56 by transfer conductors 29, and the TPIM 19 similarlytransmits electrical power to and from the second electric machine 72 bytransfer conductors 31 in response to motor torque commands for thefirst and second electric machines 56 and 72. Electrical current istransmitted to and from the ESD 74 in accordance with whether the ESD 74is being charged or discharged. TPIM 19 includes a pair of powerinverters and respective motor control modules (not shown) configured toreceive motor control commands and control inverter states therefrom forproviding motor drive or regeneration functionality.

Each of the aforementioned control modules preferably comprises ageneral-purpose digital computer generally including a microprocessor orcentral processing unit, storage mediums comprising random accessmemory, non-volatile memory, e.g., read only memory and electricallyprogrammable read only memory, a high speed clock, analog to digital anddigital to analog conversion circuitry, and input/output circuitry anddevices and appropriate signal conditioning and buffer circuitry. Eachcontrol module has a set of control algorithms, comprisingmachine-executable code and calibrations resident in the read onlymemory and executable to provide the respective functions of eachcontrol module. Each of the aforementioned control modules communicateswith other control modules, sensors, and actuators via a local areanetwork (‘LAN’) bus 6. The LAN bus 6 allows for structured communicationof control parameters and commands between the various control modules.The specific communication protocol utilized is application-specific.The LAN bus 6 and appropriate protocols provide for robust messaging andmulti-control module interfacing between the aforementioned controlmodules, and other control modules providing functionality such asantilock brakes, traction control, and vehicle stability.

Algorithms for control and state estimation in each of the controlmodules can be executed during preset loop cycles such that eachalgorithm is executed at least once each loop cycle. Algorithms storedin the non-volatile memory devices are executed by respective ones ofthe central processing units to monitor inputs from the sensing devicesand execute control and diagnostic routines to control operation of therespective device using preset calibrations. Loop cycles are executed atregular intervals, for example each 3.125, 6.25, 12.5, 25, 50 and 100milliseconds during ongoing engine and vehicle operation. Alternatively,algorithms may be executed in response to occurrence of an event.

During an engine operating cycle, i.e., a period of engine operationfrom an engine start to a subsequent engine stop, the control modulesexecute control routines to monitor and control the engine 14, includingcontrolling the engine 14 and the electro-mechanical transmission 10 tominimize a total energy loss by optimizing a total power loss whilemanaging temperatures of the engine 14 and the exhaust aftertreatmentsystem 16. This comprises executing control routines to monitor ambientoperating conditions, the engine operating conditions, and powertrainoperating conditions. The ambient operating conditions comprise anambient temperature and a barometric pressure, preferably monitored withsensing devices (not shown) on the vehicle. Vehicle operation ismonitored. The control routine includes algorithms in the form ofmachine-executable code preferably stored in the non-volatile memorydevice of one of the control modules, e.g., the HCP 5. The HCP 5executes a control routine which estimates a future energy loss for theengine operating cycle, and determines a current power loss and atime-rate of change in the estimated future energy loss for the engineoperating cycle over ranges of the engine operation.

The current total power loss (‘P_(LOSS) _(—) _(TOT)’) includes powerlosses through the electro-mechanical transmission 10 and the first andsecond electric machines 56 and 72, also referred to herein as P_(LOSS)_(—) _(OTHER), and the engine power loss, also referred to herein asP_(LOSS) _(—) _(ENG). The engine power loss comprises an estimate of thepower loss for the engine 14 at that period in time, at the currentengine operation, under the current engine operating conditions. Thisincludes monitoring and determining the engine operating conditions andthe engine operation to determine an instantaneous power loss,comprising a nominal engine power loss (‘P_(LOSS) _(—) _(ENG) _(—)_(NOM)’) for the engine operating point and a power loss correction,also referred to herein as ΔP_(LOSS ENG).

The nominal engine power loss, P_(LOSS) _(—) _(ENG) _(—) _(NOM), isdetermined using Eq. 1 set forth below.

$\begin{matrix}{P_{{LOSS\_ ENG}{\_ NOM}} = {{{\overset{.}{m}}_{EMISS} \times \left( \frac{P_{ENG}}{{\overset{.}{m}}_{EMISS}} \right)_{MAX}} - P_{ENG}}} & \lbrack 1\rbrack\end{matrix}$

wherein {dot over (m)}_(EMISS) comprises the rate of emissionsgenerated, e.g., grams of hydrocarbon for the current engine operatingconditions. The term

$\left( \frac{P_{ENG}}{{\overset{.}{m}}_{EMISS}} \right)_{MAX}$

is a constant term, derived for a specific engine design, representing amaximized engine power for a rate of emissions generation, e.g., KW-sper gram of hydrocarbon, (kW/(g/s)). An engine power term, P_(ENG),comprises the actual power produced by the engine. The differencebetween the two terms determines the nominal engine power loss, P_(LOSS)_(—) _(ENG) _(—) _(NOM).

System optimization for emissions performance is balanced againstoperation to warm-up the engine 14 and the exhaust aftertreatment system16, to achieve a minimum total energy loss over the engine operatingcycle. To minimize fuel consumption and exhaust emissions over theengine operating cycle, the optimization routine determines the futureenergy loss during the cycle.

The future energy loss, also referred to herein as E_(LOSS) _(—)_(FUTURE), comprises the amount of energy required to complete theengine operating cycle based upon what the present operating conditionsas shown by Eq. 2 set forth below.

$\begin{matrix}{E_{LOSS\_ FUTURE} = {\int_{t}^{t_{MAX}}{P_{LOSS\_ TOT}\ {t}}}} & \lbrack 2\rbrack\end{matrix}$

The limits on the integral range from current time, t, to a maximumtime, t_(MAX) during the engine operating cycle. During operation, astime t increases, the value of the integral decreases, i.e., less energyis required to warm up the exhaust aftertreatment system 16 to apreferred temperature, e.g., 600° C. This is depicted graphically withreference to FIG. 3, described herein below.

Minimizing the total energy loss comprises operating the engine tominimize the energy loss during the remainder of the engine operatingcycle, e.g., until temperature of the exhaust aftertreatment system 16reaches the preferred temperature, e.g., 600° C., or another temperaturedetermined based upon design and operating characteristics of theexhaust aftertreatment system 16. The optimization described herein isbased upon the total system power loss. The total system power lossincludes predetermined calibrations which prevent overcharging the ESD74 and determine costs for using the first and second electric machines56 and 72. This allows the system to change engine load based on theoperator torque request.

Eq. 2 can be rewritten to express the future energy loss as follows, inEq. 3 set forth below.

E _(LOSS FUTURE)(t,T _(CAT))=P _(LOSS TOT)(t,T _(CAT))×Δt+E_(LOSS FUTURE)(t+Δt,T _(CAT) +ΔT _(CAT))   [3]

wherein T_(CAT) comprises the temperature of the exhaust aftertreatmentsystem 16. This can be reduced to Eq. 4 as set forth below.

$\begin{matrix}{\frac{\left( {{- \Delta}\; E_{{LOSS}\mspace{14mu} {FUTURE}}} \right)_{T_{CAT} = {Const}}}{\Delta \; t} = {P_{LOSS\_ TOT} + \frac{\left( {\Delta \; E_{{LOSS}\mspace{14mu} {FUTURE}}} \right)_{T + {\Delta \; T}}}{\Delta \; t}}} & \lbrack 4\rbrack\end{matrix}$

Minimizing the total energy loss can be accomplished by minimizing thepower loss and the rate of change in the future energy loss. Thederivation of Eq. 4, above, can be expressed in continuous form aspartial derivatives, as set forth below in Eq. 5.

$\begin{matrix}{{- \frac{\partial E}{\partial t}} = {P_{LOSS\_ TOT} + {\frac{\partial E}{\partial T_{COOL}} \cdot \frac{T_{COOL}}{t}} + {\frac{\partial E}{\partial T_{CAT}} \cdot \frac{T_{CAT}}{t}}}} & \lbrack 5\rbrack\end{matrix}$

wherein the partial derivatives are derived for changes in energy basedupon coolant temperature and based upon temperature of the exhaustaftertreatment system 16.

The

$\frac{\partial E}{\partial T_{CAT}}$

term comprises a precalibrated factor stored as an array in memory andis determined based upon engine operating time and catalyst temperatureranging from cold, e.g., 0° C. to warmed up, e.g., 600° C. The

$\frac{\partial E}{\partial T_{COOL}}$

term comprises a precalibrated factor stored as an array in memory anddetermined as a function of engine operating time and coolanttemperature, using discrete coolant temperatures, ranging from cold,e.g., −30° C., to warmed up, e.g., 90° C. The calibration values for theengine are preferably developed using a standardized engine and vehicletest procedure. The term

$\frac{T_{CAT}}{t}$

comprises a precalibrated polynomial equation for a change intemperature of the exhaust aftertreatment system 16 based upon time forthe specific vehicle and system application. There is a plurality ofpolynomial equations for the

$\frac{T_{CAT}}{t}$

term, selected during ongoing operation based upon the engine statescomprising normal engine operation and engine operation with deactivatedcylinders. Furthermore, there are polynomial equations developed fordiscrete catalyst temperatures, ranging from cold, e.g., 0° C., towarmed up, e.g., 600° C., and above. The polynomial equations arepreferably developed using heat rejection data and a thermal model ofthe engine 14 to predict warm-up rate of the exhaust aftertreatmentsystem 16. The rate of change in the estimated future energy loss duringthe catalyst warm-up mode is determined by calculating the rate ofchange in the future energy loss based upon Eq. 5, above, anddetermining an engine operating point which comprises a minimum systempower loss, P_(LOSS) _(—) _(FINAL), or

${- \frac{\partial E}{\partial t}},$

based upon a combination of instantaneous power loss and rate of changein the future energy loss.

The nominal engine power loss, P_(LOSS) _(—) _(ENG) _(—) _(NOM), isdetermined based upon the engine operating point. The nominal enginepower loss is preferably determined during each 50 millisecond engineloop cycle, from a predetermined calibration table, determined for theengine 14 operating over a range of engine speed and load conditionsunder nominal engine operating conditions for temperature, barometricpressure and stoichiometric air/fuel ratio. The emissions power loss isevaluated using a nine-term polynomial equation with a correction basedupon temperature of the exhaust aftertreatment system 16, as describedherein. To accurately evaluate the nominal engine power loss, emissionsgeneration is estimated across all speeds and loads across an allowablerange of engine operating conditions. Changes in coolant temperature orbarometric pressure can significantly affect the estimated fuelconsumption. To account for changes in the nominal power loss due toengine operation at non-standard engine operating conditions, the enginepower loss correction, ΔP_(LOSS ENG), is added to the nominal enginepower loss P_(LOSS ENG), as depicted and described in Eq. 15,hereinbelow.

The engine power loss correction, ΔP_(LOSS ENG), is calculated basedupon the ambient operating conditions and the engine operatingconditions. A plurality of polynomial equations are reduced to programcode and ongoingly executed to calculate the power loss correction andthe future energy loss correction, based upon the engine operatingconditions, the engine operation, and the ambient operating conditions,as described herein. The power loss correction is determined based uponthe input speed, Ni, and the input torque, Ti. Each power losscorrection and future energy loss correction is determined withreference to Eq. 6 set forth below.

ΔP _(LOSS ENG) =C0+C1×Ti+C2×Ti ² +C3×Ni+C4×Ni×Ti+C5×Ni×Ti ² +C6×Ni ²+C7×Ni ² ×Ti+C8×Ni ² ×Ti ²   [6]

The engine power loss correction, ΔP_(LOSS ENG), comprises a sum of aplurality of polynomial equations described with reference to Eqs. 7-14,as follows.

A power loss related to supplemental fuel necessary for stable engineoperation under the current operating conditions is preferablycalculated using Eq. 7, as set forth below.

$\begin{matrix}{{\beta_{1}\left( {t,T_{CAT}} \right)} \times \left\lbrack {{{\overset{.}{m}}_{FUEL} \times \left( \frac{P_{ENG}}{{\overset{.}{m}}_{FUEL}} \right)_{MAX}} - P_{ENG}} \right\rbrack} & \lbrack 7\rbrack\end{matrix}$

wherein {dot over (m)}_(FUEL) is the fuel flow rate, and

$\left( \frac{P_{ENG}}{{\overset{.}{m}}_{FUEL}} \right)_{MAX}$

is the maximum power for the fuel flow rate for the engine 14, T_(CAT)comprises temperature of the exhaust aftertreatment system 16, and tcomprises elapsed time for the current engine operating cycle.

A power loss related to fueling to optimize HC emissions is preferablycalculated using Eq. 8, as set forth below.

$\begin{matrix}{{\beta_{2}\left( {t,T_{CAT}} \right)} \times \left\lbrack {{{\overset{.}{m}}_{{HC}\mspace{11mu} {EMIS}} \times \left( \frac{P_{ENG}}{{\overset{.}{m}}_{{HC}\mspace{11mu} {EMIS}}} \right)_{MAX}} - P_{ENG}} \right\rbrack} & \lbrack 8\rbrack\end{matrix}$

wherein {dot over (m)}_(HC EMIS) is a fuel flow rate for HC emissions,and

$\left( \frac{P_{ENG}}{{\overset{.}{m}}_{{HC}\mspace{11mu} {EMIS}}} \right)_{MAX}$

is the maximum power for the fuel flow rate for optimized HC emissionsfor the engine 14.

A power loss related to fueling to optimize NO_(x) emissions ispreferably calculated using Eq. 9, as set forth below.

$\begin{matrix}{{\beta_{3}\left( {t,T_{CAT}} \right)} \times \left\lbrack {{{\overset{.}{m}}_{{NOx}\mspace{14mu} {EMIS}} \times \left( \frac{P_{ENG}}{{\overset{.}{m}}_{{NOx}\mspace{14mu} {EMIS}}} \right)_{MAX}} - P_{ENG}} \right\rbrack} & \lbrack 9\rbrack\end{matrix}$

wherein {dot over (m)}_(NOx EMIS) is a fuel flowrate for NOx emissions,and

$\left( \frac{P_{ENG}}{{\overset{.}{m}}_{{NOx}\mspace{14mu} {EMIS}}} \right)_{MAX}$

is a maximum power for the fuel flow rate for optimized NOx emissionsfor the engine 14.

The future energy loss related to fueling to effect coolant and engineoil warm-up is preferably calculated using Eq. 10, as follows:

$\begin{matrix}{{\beta_{4}\left( {t,T_{CAT}} \right)} \times \frac{{E_{FUEL}\left( {t,T_{COOL}} \right)}}{T_{COOL}} \times \frac{{T_{COOL}\left( {{Ni},{Ti},T_{COOL}} \right)}}{t}} & \lbrack 10\rbrack\end{matrix}$

The future energy loss related to fueling to effect warm-up of theexhaust aftertreatment system to meet HC emissions is preferablycalculated using Eq. 11, as set forth below.

$\begin{matrix}{{\beta_{5}\left( {t,T_{CAT}} \right)} \times \frac{{E_{HC}\left( {t,T_{CAT}} \right)}}{T_{CAT}} \times \frac{{T_{CAT}\left( {{Ni},{Ti},T_{CAT}} \right)}}{t}} & \lbrack 11\rbrack\end{matrix}$

The future energy loss related to fueling to effect warm-up of theexhaust aftertreatment system to meet NO_(x) emissions is preferablycalculated using Eq. 12, as set forth below.

$\begin{matrix}{{\beta_{6}\left( {t,T_{CAT}} \right)} \times \frac{{E_{NOx}\left( {t,T_{CAT}} \right)}}{T_{CAT}} \times \frac{{T_{CAT}\left( {{Ni},{Ti},T_{CAT}} \right)}}{t}} & \lbrack 12\rbrack\end{matrix}$

The future energy loss related to fueling to manage the exhaustaftertreatment system 16 temperature is preferably calculated using Eq.13, as set forth below.

$\begin{matrix}{{\beta_{7}\left( {t,T_{CAT}} \right)} \times \frac{{T_{CAT}\left( {{Ni},{Ti},T_{CAT}} \right)}}{t}} & \lbrack 13\rbrack\end{matrix}$

The future energy loss related to fueling to prevent engineover-temperature operation is preferably calculated using Eq. 14, as setforth below.

$\begin{matrix}{{\beta_{8}\left( {t,T_{CAT},T_{COOL}} \right)} \times \frac{{T_{COOL}\left( {{Ni},{Ti},T_{COOL}} \right)}}{t}} & \lbrack 14\rbrack\end{matrix}$

The terms in Eqs. 7-14 are precalibrated and stored as arrays in one ofthe memory devices of the HCP 5, based upon the engine and ambientoperating conditions and the engine operation. The term T_(COOL)comprises the coolant temperature. The terms E_(FUEL), E_(HC), andE_(NOX) comprise energy losses related to supplemental fueling to meetHC and NO_(x) emissions. The

$\frac{{T_{COOL}\left( {{Ni},{Ti},T_{COOL}} \right)}}{t}\mspace{14mu} {and}\mspace{14mu} \frac{{T_{CAT}\left( {{Ni},{Ti},T_{CAT}} \right)}}{t}$

terms comprise precalibrated time-based changes in temperatures whichvary with the input speed, torque, and corresponding temperature. Theterms

$\frac{{E_{HC}\left( {t,T_{CAT}} \right)}}{T_{CAT}}\mspace{14mu} {and}\mspace{14mu} \frac{{E_{NOx}\left( {t,T_{CAT}} \right)}}{T_{CAT}}$

are precalibrated changes in energy based upon the temperature of theexhaust aftertreatment system 16 which vary with elapsed time, t, andthe temperature of the exhaust aftertreatment system 16, and arepreferably based on off-line energy loss calculations. The term

$\frac{{T_{COOL}\left( {{Ni},{Ti},T_{COOL}} \right)}}{t}$

comprises a time-rate change in coolant temperature based upon speed,load, and the coolant temperature.

The coefficients β₁-β₈ comprise weighting factors for the power lossequations, i.e., Eqs. 7-14, and are determined for the range of elapsedengine run times, t, for the engine operating cycle, and temperatures ofthe exhaust gas aftertreatment system 16, T_(CAT), and coolanttemperatures, T_(COOL). The coefficients β₁-β₈ are preferably calibratedand evaluated using a least squares curve fit using engine data. Thecoefficients β₁-β₈ are stored in calibration tables within ROM forvarious operating conditions and retrievable during the ongoing engineoperation. Preferably, the coefficients are calibrated such thatβ₁+β₂+β₃=1, β₄+β₅+β₆=1, β₁=β₄, β₂=β₅, and β₃=β₆. As described hereinbelow with reference to FIGS. 3A and 3B, the β₇ coefficient comprises apredetermined calibration for controlling engine operation to manage thetemperature of the exhaust aftertreatment system 16. Managing thetemperature of the exhaust aftertreatment system 16 using this methodreduces or eliminates a need for operating the engine 14 under fuelenrichment conditions to manage catalyst temperature. The β₈ term is asubjective calibration used to manage engine operation (speed and load)to manage the coolant temperature. Linear interpolation is used todetermine the coefficients when the operating conditions are betweentable values.

Each of Eqs. 7-14 is executed in a form of Eq. 6, with specificallycalibrated coefficients C0-C8, and the input speed, Ni, and the inputtorque, Ti. The coefficients C0-C8 for each of Eqs. 7-14 are preferablycalibrated and evaluated using a least squares curve fit derived usingengine data generated over the ranges of input speeds, Ni, and loads,Ti, during engine operation in the operating states and the operatingmodes. Thus, a set of coefficients C0-C8 are generated for the air/fuelratio operating modes comprising each of the stoichiometric and the richoperating modes, e.g., an air/fuel ratio equivalence of 1.0 and 0.7, andfor each of the engine temperature management modes comprising thewarm-up and the warmed up modes. A set of coefficients C0-C8 are furthergenerated for each of the normal engine state and the cylinderdeactivation state. A set of coefficients C0-C8 are further derived foreach of a standard and a low barometric pressure, e.g., 100 kPa and 70kPa. The aforementioned sets of coefficients C0-C8 can be stored inarrays within one of the memory devices for each of the operating modesand engine states, for retrieval during ongoing operation. As described,there are eight sets of coefficients C0-C8 generated and stored. Theaddition of the polynomial equations for the engine power loss reflectedin Eqs. 7-14 results in the power loss correction to the standard powerloss calculation.

The polynomial coefficients C0-C8 are evaluated for each of Eqs. 7-14during ongoing operation and then added to generate a single set ofcoefficients C0-C8 for use with Eq. 6, and updated at a relatively slowrate of once per second. The β₁-β₈ weighting factors determine theweighting between the different types of engine power loss, as describedhereinbelow. The final polynomial equation is evaluated hundreds oftimes every second as an element of torque optimization routines.Determining a power loss at a specific engine operating condition cancomprise determining power loss using equations described herein andinterpolating therebetween to determine power loss at the real-timeoperating conditions.

The control routine determines the total engine power loss by summingthe nominal power loss and power loss correction, as set forth below inEq. 15.

P _(LOSS) _(—) _(ENG) _(—) _(TOT) =P _(LOSS ENG) +ΔP _(LOSS ENG)   [15]

The nominal engine power loss is determined as described in Eq. 1, andthe power loss correction is determined as described in Eq. 6 withcoefficients C0-C8 determined by combining results from Eqs. 7-14,determined based upon the current engine operation and the engine andambient operating conditions, as previously described. This operationpermits including complex engine power loss characteristics to calculatea single engine power loss. The final C0-C8 coefficients to thepolynomial equation of Eq. 6 are determined based on precalibratedfactors and the β₁-β₈ weighting factors. This determination of thecoefficients C0-C8 can be performed at a relatively slow update rate,e.g., once per second. The final polynomial equation is used in theoptimization routine numerous times before the next update.

Thus, the total power loss P_(LOSS) _(—) _(TOT) can be determined as setforth below in Eq. 16.

P _(LOSS) _(—) _(TOT) =P _(LOSS ENG) +ΔP _(LOSS ENG) +P _(LOSS) _(—)_(OTHER)   [16]

Referring now to FIG. 2, an exemplary minimization routine is depictedfor determining the minimum total power loss, P_(LOSS) _(—) _(TOT) tominimize the total energy loss. The minimization routine is executed todetermine a preferred engine operation to minimize the total enginepower loss. The minimization routine preferably comprises execution of atwo-dimensional search engine 260 which has been encoded in the HCP 5.The two-dimensional search engine 260 iteratively generates engineoperating points ranging across allowable engine operating points. Theengine operating points comprise the input speed and input torque [Ni,Ti]_(j) and the ranges are within minimum and maximum input speeds andinput torques (‘NiMin’, ‘NiMax’, ‘TiMin’, ‘TiMax’). The minimum andmaximum input speeds and input torques can comprise achievable inputspeeds and input torques, e.g., from engine idle operation to enginered-line operation, or may comprise a subset thereof wherein the rangesare limited for reasons related to operating characteristics such asnoise, vibration, and harshness.

The generated engine operating points [Ni, Ti]_(j) are executed in aniterative loop 266. The subscript “j” refers to a specific iteration,and ranges in value from 1 to n. The quantity of iterations n can begenerated by any one of a number of methods, either internal to thesearch engine, or as a part of the overall method. The iterative loop266 comprises inputting each of the generated engine operating points[Ni, Ti]_(j) to a system equation 262, from which a value for the totalpower loss (P_(LOSS) _(—) _(TOT))_(j) is determined for the specificiteration. The system equation 262 comprises an algorithm which executesEq. 16, above. In the engine operating cycle when it is determined thatthe temperature of the exhaust aftertreatment system 16 is less than apreferred temperature, e.g., during a cold-start, β₂=1 as used in Eq. 8,and β₁=0 and β₃=0, β₅=1, and β₄=0 and β₆=0, and a set of thecoefficients C0-C8 are derived as described hereinabove.

The total power loss (P_(LOSS) _(—) _(TOT))_(j) determined for thespecific iteration is returned and captured, or analyzed, in thetwo-dimensional search engine 260 depending upon specifics thereof. Thetwo-dimensional search engine 260 iteratively evaluates values for thetotal power loss, (P_(LOSS) _(—) _(TOT))_(j) and selects new values for[Ni, Ti] based upon feedback to search for a minimum total power loss.The two-dimensional search engine 260 identifies preferred values for[Ni, Ti] at a preferred power loss, i.e., a minimum total power loss,(P_(LOSS) _(—) _(TOT))_(j) derived from all the iteratively calculatedvalues. The preferred total power loss and corresponding values forinput speed and input torque, [Ni, Ti, P_(LOSS) _(—) _(TOT)]_(pref), areoutput from the HCP 5 to the ECM 23. The ECM 23 converts the preferredinput speed and input torque [Ni, Ti]_(pref) to a corresponding engineoperating point comprising engine speed and torque [N_(E),T_(E)]_(pref), which the ECM 23 uses to control operation of the engine14.

As previously mentioned, there is a plurality of executable power losscorrection polynomial equations. In the exemplary embodiment, there areeight sets of polynomial equations, derived for combinations of engineoperation comprising: air/fuel ratio control modes of rich andstoichiometric, i.e., an air/fuel equivalence ratio of about 0.7 (rich)and 1.0 (stoichiometry); the normal engine state and the cylinderdeactivation state; and, engine operating temperature comprising thewarm-up mode and the warmed-up mode, i.e., coolant temperature at orabout 90° C. In operation, the engine system monitors ongoing operation,including engine speed (RPM), load (brake torque or NMEP in N-m),barometric pressure, coolant temperature, and air/fuel ratio.

Referring to FIGS. 3A and 3B, a calibration assigning a value to the β₇term based upon the temperature of the exhaust aftertreatment system 16is depicted. The β₇ term is used in Eq. 13, above, and comprises acalibration for controlling engine operation (speed and load) to managethe temperature of the exhaust aftertreatment system 16. FIG. 3A depictscalibration values for the β₇ term when the engine 14 is aspark-ignition engine intended to operate at stoichiometry. The β₇ termvaries based upon the temperature, T_(CAT), of the exhaustaftertreatment system 16. This includes values for the β₇ term for thetemperature of the exhaust aftertreatment system 16 ranging from coldstart operation (‘Cold Start’), light-off of one of the elements of theexhaust aftertreatment system 16 (‘Light-Off’), normal, ongoingoperation (‘Normal Operation’), and at temperatures which can result inthermal damage to one of the elements of the exhaust aftertreatmentsystem 16 (‘Catalyst Damage’).

During each engine operating cycle, the control modules execute thecontrol routines to monitor and control the engine 14 and theelectro-transmission 10 to minimize total energy loss by optimizing thetotal power loss while effecting warm-up of the engine 14 and managingtemperature of the exhaust aftertreatment system 16. This includesdetermining the temperature of the one of the elements of the exhaustaftertreatment system 16. When the control routine determines that theexhaust aftertreatment system 16 is below a preferred temperature, e.g.,during a cold start operating cycle, the control routine identifies apreferred engine operation to achieve the preferred temperature whileminimizing the total energy loss. Operation of the engine 14 iscontrolled to achieve the preferred temperature of the exhaustaftertreatment system 16. The electro-mechanical transmission 10 iscontrolled to achieve the tractive power comprising a torque and speedoutput through the output member 64 based upon the preferred engineoperation and the operator torque request, among other factors. Thepreferred engine operation to achieve the preferred temperature andminimize the total energy loss includes estimating the future energyloss and determining the power loss and the rate of change in theestimated future energy loss, and determining the preferred engineoperation to minimize the power loss and the rate of change in theestimated future energy loss.

The overall strategy comprises adjusting operation of the engine 14 in amanner which increases the temperature of the exhaust aftertreatmentsystem 16 when the exhaust aftertreatment system 16 is relatively cool,and adjusting operation of the engine 14 in a manner which decreases thetemperature of the exhaust aftertreatment system 16 when the exhaustaftertreatment system 16 is relatively high. Thus, during a cold startand a warm-up operation the β₇ term is negative. Operation of the engine14, in terms of input speed and torque, Ni and Ti, can be adjusted toincrease exhaust gas temperature and thermally heat the exhaustaftertreatment system 16. The overall tractive power output from thehybrid powertrain remains unchanged during the operation of the engine14 to heat the exhaust aftertreatment system 16. However, the controlsystem can channel a portion of the engine output power into one of thefirst and second electric machines 56 and 72 for electric charging andincreasing a state of charge of the ESD 74. The β₇ term increases whenthe control system determines that light-off of one of the elements ofthe exhaust aftertreatment system 16 has occurred. When the exhaustaftertreatment system 16 reaches the preferred temperature range, the β₇term is maintained at or near zero and the engine operation iscontrolled for minimum power loss and optimum fuel economy. When it isdetermined that the exhaust aftertreatment system 16 is outside thepreferred temperature range, e.g., is approaching or has reached atemperature which can cause thermal damage, the β₇ term is adjustedpositively to adjust the input speed and torque Ni and Ti to decreasethe temperature of the exhaust gas feedstream temperature and decreaseheat transfer to the exhaust aftertreatment system 16. The controlsystem operates the first and second electric machines 56 and 72 togenerate sufficient tractive torque to meet the operator torque requestduring this operation.

FIG. 3B depicts calibration values for the β₇ term when the engine 14comprises a compression-ignition engine, or a spark-ignition enginewhich spends a portion of its operation at a lean air/fuel ratio. FIG.3B is analogous to FIG. 3A, and also depicts calibration values for theβ₇ term for operating engine 14 to generate an exhaust gas feedstreamwhich can be used to regenerate a lean NOx adsorber or purge aparticulate matter filter device (‘Regen’). This can include achievingan exhaust gas feedstream temperature above 600° C. and a rich air/fuelratio for a period of time. Thus, the β₇ term can be reduced to anegative number for a period of time to effect operation of the engine14. Controlling the temperature of the exhaust aftertreatment system 16in this manner can eliminate a need for operating the engine 14 underfuel enrichment conditions to manage temperature of the exhaustaftertreatment system 16.

The minimization routine described hereinabove can be applied topowertrain systems consisting of an engine and transmission systemwherein the engine 14 can be selectively deactivated and reactivatedduring the vehicle operating cycle and the operating point of the engine14 can be managed independently from the tractive power output throughthe output member 64 of the transmission 10. Another embodiment of thepowertrain system is referred to as a belt-alternator-starter system.Using the control system described hereinabove with reference to FIGS. 2and 3A and 3B, the minimization routine can be executed to determine apreferred engine operation to minimize the total power loss P_(LOSS)_(—) _(TOT) and minimize the total energy loss. The two-dimensionalsearch engine 260 iteratively generates engine operating points rangingacross the allowable engine operating points. The engine operatingpoints comprise the input speed and input torque (‘[Ni/Ti]_(j)’) and theranges are within minimum and maximum input speeds and input torques(‘NiMin’, ‘NiMax’, ‘TiMin’, ‘TiMax’). The minimum and maximum inputspeeds and input torques can comprise achievable input speeds and inputtorques, e.g., from engine idle operation to engine red-line operation.The input speed and input torque to the input member 12 can be adjustedand optimized, and tractive speed and power output from the transmission10 can be managed by selectively controlling gearing of the transmission10.

The disclosure has described certain preferred embodiments andmodifications thereto. Further modifications and alterations may occurto others upon reading and understanding the specification. Therefore,it is intended that the disclosure not be limited to the particularembodiment(s) disclosed as the best mode contemplated for carrying outthis disclosure, but that the disclosure will include all embodimentsfalling within the scope of the appended claims.

1. Method for controlling an internal combustion engine during an engineoperating cycle, said engine fluidly connected to an exhaustaftertreatment system and operatively connected to an electro-mechanicaltransmission to transmit tractive power to a driveline, comprising:determining a temperature of the exhaust aftertreatment system;adjusting power output of the engine based upon the temperature of theexhaust aftertreatment system and a preferred temperature range of theexhaust aftertreatment system; and, controlling the electro-mechanicaltransmission to transmit tractive power to the driveline to meet anoperator torque request based upon the adjusted power output of theengine.
 2. The method of claim 1, further comprising increasing theengine power output when a temperature of an element of the exhaustaftertreatment system is less than the preferred temperature range ofthe exhaust aftertreatment system.
 3. The method of claim 1, furthercomprising increasing the engine power output to increase temperature ofthe exhaust aftertreatment system for a period of time to achieve apredetermined temperature effective to regenerate an element of theexhaust aftertreatment system.
 4. The method of claim 1, furthercomprising decreasing the engine power output when the temperature ofthe exhaust aftertreatment system exceeds the preferred temperaturerange of the exhaust aftertreatment system.
 5. The method of claim 1further comprising determining a preferred engine operation to achievethe preferred temperature range of the exhaust aftertreatment system andminimize a total energy loss.
 6. The method of claim 1, furthercomprising estimating a future energy loss; determining a total powerloss and a rate of change in the estimated future energy loss; anddetermining a preferred engine operation to minimize the total powerloss and the rate of change in the estimated future energy losseffective to achieve the preferred temperature range of the exhaustaftertreatment system and minimize the total energy loss during theengine operating cycle.
 7. The method of claim 6, further comprising:iteratively generating a plurality of engine speed states and enginetorque states, and calculating a corresponding plurality of total powerlosses and rates of change in the estimated future energy loss;determining minimum ones of the plurality of total power losses andrates of change in the estimated future energy loss; and determining thepreferred engine operation comprising the engine speed state and enginetorque state corresponding to the minimum ones of the plurality of totalpower losses and the rates of change in the estimated future energyloss.
 8. The method of claim 7, wherein the preferred engine operationfurther comprises an engine state comprising one of an all-cylinderoperation and a cylinder-deactivation operation.
 9. The method of claim8, wherein the preferred engine operation further comprises an engineoperating mode comprising one of a stoichiometric air/fuel ratiooperation and a rich air/fuel ratio operation.
 10. The method of claim7, further comprising executing a two-dimensional search engine toiteratively generate the plurality of engine speed states and enginetorque states.
 11. The method of claim 7, wherein total power lossesinclude engine power losses and other powertrain losses.
 12. The methodof claim 11, wherein the engine power losses comprise nominal enginepower losses and power loss corrections.
 13. The method of claim 12,wherein the power loss corrections are based upon an engine air/fuelratio mode, an engine cylinder deactivation state, and, an engineoperating temperature mode.
 14. Method for controlling an internalcombustion engine during an engine operating cycle, said engineoperatively connected to an electro-mechanical transmission, comprising:monitoring ambient operating conditions and engine operating conditions;determining a temperature of an exhaust aftertreatment system fluidlyconnected to the engine; adjusting power output of the engine based uponthe temperature of the exhaust aftertreatment system and a preferredtemperature of the exhaust aftertreatment system; and controlling theelectro-mechanical transmission based upon the adjusted power output ofthe engine.
 15. The method of claim 14, further comprising controllingthe electro-mechanical transmission to transmit tractive power to thedriveline based upon the adjusted power output of the engine.
 16. Themethod of claim 15, further comprising controlling theelectro-mechanical transmission to generate electric power based uponthe adjusted power output of the engine.
 17. The method of claim 14,further comprising: estimating a future energy loss during the engineoperating cycle; determining a power loss and a rate of change in theestimated future energy loss during the engine operating cycle; anddetermining a preferred engine operation to minimize the power loss andthe rate of change in the estimated future energy loss effective toachieve the preferred temperature of the exhaust aftertreatment systemand minimize the total energy loss during the engine operating cycle.18. The method of claim 17, further comprising: iteratively generatingengine speed states and engine torque states; calculating a power lossand a rate of change in the estimated future energy loss for each of theiteratively generated engine speed states and engine torque states;determining a minimum value for the calculated power loss and the rateof change in the estimated future energy loss; and determining thepreferred engine operation comprising an engine speed state and anengine torque state corresponding to the minimum value for thecalculated power loss and the rate of change in the estimated futureenergy loss.
 19. Method for controlling an internal combustion enginefluidly connected to an exhaust aftertreatment system and operativelyconnected to a transmission, comprising: determining a temperature ofthe exhaust aftertreatment system; adjusting an engine speed state andan engine torque state based upon the temperature of the exhaustaftertreatment system and a preferred temperature range of the exhaustaftertreatment system to minimize a total energy loss during an engineoperating cycle; controlling the engine to the adjusted engine speedstate and engine torque state to achieve the preferred temperature ofthe exhaust aftertreatment system; and controlling the transmission totransmit tractive power to the driveline to meet an operator torquerequest based upon the preferred engine operation.
 20. The method ofclaim 19, further comprising: estimating a future energy loss for theengine operating cycle; determining a power loss and a rate of change inthe estimated future energy loss; and adjusting the engine speed stateand an engine torque state to minimize the power loss and the rate ofchange in the estimated future energy loss effective to achieve thepreferred temperature of the exhaust aftertreatment system and minimizethe total energy loss.
 21. The method of claim 20, wherein determiningthe adjusted engine speed state and an engine torque state comprises:iteratively generating engine speed states and engine torque states;calculating a power loss and a rate of change in the estimated futureenergy loss for each of the iteratively generated engine speed statesand engine torque states; determining a minimum value for the calculatedpower loss and the rate of change in the estimated future energy loss;and determining a preferred engine operation comprising an engine speedstate and an engine torque state corresponding to the minimum value forthe calculated power loss and the rate of change in the estimated futureenergy loss.